Hey, just to update, it seems like Mint itself could be the one holding a setting somewhere that prevents the mouse wheel to work. This person was able to activate the feature with the scrollwheel but using plain Debian:

as you can from the link you provided, that feature isn't enabled in plain debian either, but apparently it's easy to do so (it's in link)

open up gconf-editor(type gconf-editor in term) and that will pop up the GUI for editing gconf. Go into /apps/gwd and you see where it says ‘mouse_wheel_action’ and the field to the right of it says ‘none’ ? Yea, well double click on the none and replace the word ‘none’ with the word ‘shade’

Launching fallback window managerWindow manager warning: "" found in configuration database is not a valid value for keybinding "switch_to_workspace_1"Window manager warning: "" found in configuration database is not a valid value for keybinding "cycle_windows"